From the Wikipedia page on Isaak Yaglom:

the breadth of his interests was truly extraordinary: he was seriously interested in history and philosophy, passionately loved and had a good knowledge of literature and art, often came forward with reports and lectures on the most diverse topics (for example, on Blok, Akhmatova, and the Dutch painter Escher), actively took part in the work of the cinema club in Yaroslavl and the music club at the House of Composers in Moscow, and was a continual participant of conferences on mathematical linguistics and on semiotics

From this interview of John Baez:

Learn a lot. Try to understand how the whole universe works, from the philosophical, logical, mathematical and physical aspects to chemistry, biology, and the sciences based on those, to the historical sciences such as cosmology, paleontology, archaeology and history, to the social sciences such as psychology, sociology, anthropology, politics and economics, to the aspects that are captured best in literature, art and music.

It’s a never-ending quest, and obviously it pays to specialize and become more of an expert on a few things – but the more angles you can take on any subject, the more likely you are to stumble on good questions or good answers to existing questions. Also, when you get stuck on a problem, or get tired, it can be really re-energizing to learn new things.

L Mahadevan:

Problems in nature and technology, as we know well, do not come neatly packaged into “quantum, statistical, classical and continuum,…” any more than they come packaged into “biological, chemical, physical, mechanical, electrical, … ” categories. It is us humans who incapable as we are of comprehending the larger whole who break up the questions into bite sized pieces … but rarely are able to put back the pieces into a whole.